This depends on which basic mode you choose (Light palette Classic (EU), Light Palette Classic (US), etc.) during setup (or in the system settings).
I usually set-up the desk to have the colours mean:
Blue for levels going up
Green for levels going down
Magenta for levels staying the same
(Blue as the sky, green as grass, and a magenta horizon)

(Then there is yellow for levels affected by subs, white for blocked levels)